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Home , Dwarf sperm whale, Killer whale, Orcinus, Sperm whale

Journal of the Marine Biological Association of the United Kingdom, page 1 of 5. # Marine Biological Association of the United Kingdom, 2013 doi:10.1017/S0025315413000908 Killer ( orca) occurrence and in the Bahamas charlotte dunn and diane claridge Bahamas Marine Research Organisation, PO Box AB-20714, Marsh Harbour, Abaco, Bahamas

Killer (Orcinus orca) have a cosmopolitan distribution, yet little is known about populations that inhabit tropical waters. We compiled 34 sightings of killer whales in the Bahamas, recorded from 1913 to 2011. Group sizes were generally small (mean ¼ 4.2, range ¼ 1–12, SD ¼ 2.6). Thirteen sightings were documented with photographs and/or video of suffi- cient quality to allow individual photo-identification analysis. Of the 45 whales photographed, 14 unique individual killer whales were identified, eight of which were re-sighted between two and nine times. An adult female (Oo6) and a now-adult male (Oo4), were first seen together in 1995, and have been re-sighted together eight times over a 16-yr period. To date, killer whales in the Bahamas have only been observed preying on marine , including Atlantic spotted ( frontalis), Fraser’s dolphin (Lagenodelphis hosei), pygmy ( breviceps) and (Kogia sima), all of which are previously unrecorded prey for Orcinus orca.

Keywords: killer whales, Bahamas, predation, Atlantic, Orcinus orca

Submitted 30 December 2012; accepted 15 June 2013

INTRODUCTION encounters with killer whales documented during dedicated surveys. Since 1991, marine mammal sight- Killer whales are predominantly temperate or cold water species ing reports have been obtained through a public sighting and much is known about their distribution, behavioural ecology network established and maintained by the Bahamas Marine and localized abundance in colder climes (Forney & Wade, Mammal Research Organization (BMMRO). This forum has 2007). Although known to occur in the tropics (Leatherwood increased public awareness of marine mammals locally and &Dalheim,1978; Olson & Gerrodette, 2008), their occurrence created a platform for citizen science to contribute to a data- in lower latitudes is not considered to be common in the base of cetacean sightings in the Bahamas, currently consisting north-west Atlantic (Katona et al., 1988; Reeves & Mitchell, of 22 species. In addition, dedicated opportunistic and line 1988), as evidenced by the scarcity of published accounts. transect vessel surveys have been conducted in the northern Existing records of occasional sightings and strandings of killer Bahamas since 1991, mostly concentrated around Abaco whales in the waters of the wider comprise reports Island (Figure 1), for the purpose of documenting the behav- covering much of the region including Florida (Moore, 1953), ioural ecology, distribution and abundance of cetaceans in the Dominican Republic (Mattila et al., 1994), Puerto Rico local waters. Survey effort covered approximately 5000 km (Winn et al., 1979), the Virgin Islands (Erdman, 1970)and of track line annually in both pelagic and coastal habitats (Evans, 1997). There were also a small number of and has occurred year-round since 2001. killer whales taken in the St Vincent fisheries between 1967 During encounters, data were collected on species, group and 1974 (Caldwell & Caldwell, 1975). size and composition, and behaviour state of the , In the Bahamas, although sightings have been and each was photographed as described by Bigg documented from as early as 1913 (Murphy, 1947), only one (1982), for the purposes of species confirmation and individ- published record exists since that initial published account ual identification. Additionally, both photographic and video (Backus, 1961). Here we summarize all reported sightings in recordings were used to document observations of killer the Bahamas, including re-sightings of individuals, and docu- whale feeding behaviour and prey species when feasible. ment four new species of cetacean prey. Predation events were determined by directly observing killer whales killing an animal, including surfacing with prey parts in their mouths. Acoustic recordings were taken when- ever possible during encounters, using a hydrophone at a MATERIALS AND METHODS depth of 10 m recording to an M-Audio Microtrack II digital recorder with a frequency response of 0.5 dB from Killer whale sightings from throughout the Bahamas were col- 20 Hz to 20 kHz and a sampling rate of 96 kHz. lated from a variety of sources. Primary data sources included A catalogue of photographically identified killer whales was sightings reported via a public sighting network and created from all documented killer whale encounters in the Bahamas. High quality photographs of individual whales

Corresponding author: were examined for key identifying characteristics including C. Dunn the dorsal fin, saddle and eye patch. All photographs and cap- Email: [email protected] tured video stills of individual killer whales were compared to

1 2 charlotte dunn and diane claridge

the catalogue, allowing individual animals to be repeatedly identified both within and across survey years and regions, and new individuals to be added to the catalogue chronologi- cally upon discovery. In addition to reviewing the published literature for killer whale sightings in the Bahamas, we also conducted an exten- sive search of local fishing websites and blogs, and requested photographs and videos of opportunistic encounters from individuals when their contact information was available.

RESULTS

The first reported sighting of a killer whale in Bahamian waters was from the ship ‘Grace’ in 1913 (Murphy, 1947), and the first photographic evidence was of a stranded killer whale at Man O’War Cay in the northern Bahamas in 1960 (Backus, 1961). Contemporary records include an additional 32 sightings throughout the Bahamas and adjacent Fig. 1. Killer whale sightings (black circles) in the Bahamas and adjacent waters (Figure 1). Thirteen of these records include photo- waters from 1913 to 2012. The 1000 m isobath is indicated in blue. See online publication for colour figure: doi: 10.1017/S0025315413000908 graphs and/or video of sufficient quality to allow identification of individual animals (Table 1). Despite the lack of documen- ted evidence from the remaining 19 encounters, species

Table 1. Killer whale sightings in the Bahamas from 1913 to 2011. Seasonality is indicated by month–year . For each encounter group size, prey taken, whale ID numbers, whether photographs or video were collected, and the information sources are indicated. Species abbreviations are: Sf, Atlantic (Stenella frontalis); Lh, Fraser’s dolphin (Lagenodelphis hosei); Ks, dwarf sperm whale (Kogia sima); Kb, (K. brevi- ceps); Ksp, unknown Kogia species. ‘BMMRO’ indicates data collected during dedicated cetacean surveys.

Month Year Group size Prey Whale ID Photos or video? Source

1939 1 N Mowbray, 1939 Apr 1968 6 N CETAP, 1982 Apr 1981 3 N Reeves & Mitchell, 1988 Apr 2008 2 Y Public report May 1994 3 Y Public report May 1995 6 N Public report May 1998 1 N Public report May 2003 2 N Public report Jun 1960 1 Y Backus, 1961 Jun 1996 6 4 Y Public report Jun 1996 3 N Public report Jun 1997 2 N Public report Jun 2001 7 Lh & Ks 1, 2, 4, 6, 7, 8, 9 Y BMMRO Jun 2006 3 4, 6 Y Public report Jun 2008 3 N Public report Jul 1987 6 Ksp. 2, 10 Y Public report Jul 1993 6 Y Public report Jul 1995 6 Sf 1, 2, 3, 4, 5, 6 Y BMMRO Jul 2001 3 Kb Y Public report Jul 2003 3 N Public report Jul 2005 4 Ks 1, 7, 9, 13 Y BMMRO Jul 2007 3 Y Public report Jul 2009 4 2, 4, 6, 14 Y BMMRO Jul 2010 4 2, 4, 6, 14 Y BMMRO Aug 1913 7 N Murphy, 1947 Aug 2002 12 11 Y Public report Aug 2007 6 N Public report Aug 2008 2 N Public report Aug 2011 4 2, 4, 6, 14 Y Public report Aug 2011 4 2, 4, 6, 14 Y Public report Sep 2011 4 2, 4, 6, 14 Y Public report Oct 1991 12 11, 12 Y Public report Nov 2007 3 Y Public report Nov 2010 2 Y Public report killer whales in the bahamas 3 identification is considered to be sufficiently reliable due to the small calf. When the killer whales were approximately 0.5 km gross morphologically diagnostic characteristics unique to away, the sperm whales formed a rosette with their heads killer whales. Killer whale sightings were reported during oriented inwards, and appeared to be protecting the calf, at every month from April through to November, although the the centre of this formation. Once the formation was com- majority of sightings were recorded in May through to plete, a young male sperm whale with an erect penis breached August; none were reported during December through to three times in succession, during which time the killer whales March. Group sizes were generally small with a mean of 4.2 turned approximately 458 away from the sperm whale group, whales (range ¼ 1–12, SD ¼ 2.6). increased their speed and swam away. The sperm whale be- Forty-five whales were photo-identified from the 13 haviour during this encounter was remarkably similar to encounters. After photographic comparisons among all that described by Pitman et al. (2001) during a fatal attack encounters, 14 unique individual killer whales were identified, on sperm whales by killer whales off the coast of central eight of which were re-sighted an average of five times , although here the killer whales did not attack. (range ¼ 2–9), representing at least one matriline. The most Moreover, no predation was observed during an encounter frequently sighted whale was an adult male (Oo4), first with a group of four killer whales in the waters off south-west encountered in 1995 off the Atlantic side of Abaco Island, in Abaco Island in 2010, only approximately 8 km away from the northern Bahamas, and subsequently re-sighted eight locations in south-west Abaco where killer whales have been more times over a 10-yr period (2001 to 2011). Of particular observed preying on marine mammals. In 2010, behavioural note were sightings of this whale off south-west Abaco Island and photographic data were collected over a period of 7 h in June 2001, and only 5 km away from this location eight during which the killer whale group was followed off the years later, in July 2009. During eight of the nine encounters south-west coast of Abaco Island and visual contact was main- that included Oo4 between 1995 and 2011, he was observed in tained. During the course of the encounter, the killer whales a group of whales that included the adult female Oo6 who were silent, with real-time listening to the hydrophone docu- was seen with two different calves during this period menting no sounds, and post-analysis of recordings made (Table 1). Based on the high rate of co-occurrence of these whilst in the presence of the killer whales having recorded two whales, and longitudinal data including genealogical no sounds either. The whales remained in a tight formation, studies of killer whales in the eastern North Pacific documenting and travelled slowly in a primarily directional course through- natal fidelity to social groups (Baird & Whitehead, 2000), it is out the encounter, passing within 1 km of three different likely that this pair consists of a female and her male offspring. groups of Blainville’s beaked whales, and four groups of Killer whales were observed preying on four species of Kogia sp. without any obvious alteration of their course of marine mammals during five encounters, and three of these travel or behavioural state. There was an occasional zig-zag encounters were documented by BMMRO’s field team pattern to their track but this was believed to be avoidance (Table 1). Prey species identified included Atlantic spotted of the research vessel during close approaches to obtain dolphin (Stenella frontalis), Fraser’s dolphin (Lagenodelphis photographs. hosei), dwarf sperm whale (Kogia sima) and pygmy sperm During three encounters (2001, 2009 and 2010), we whale (K. breviceps). In four out of these five encounters, the deployed a hydrophone to listen for killer whale sounds killer whales preyed on Kogia species (Table 1). Two of the immediately before, during and after prey captures, as well killer whales present during the June 2001 encounter were as during periods when the whales were travelling slowly. also present in the 2005 encounter, and the encounter Killer whale sounds were recorded in 2001 following preda- locations for these two events were less than 2 km apart. tion on a dwarf sperm whale by seven killer whales, but no During both of these encounters, the killer whales predated killer whale sounds were recorded during all other events, upon dwarf sperm whales (Figure 2). both before, during and after obvious predation events, as In 2009, a group of four killer whales approached a group well as during slow travel as exhibited in 2010. of seven sperm whales ( macrocephalus) containing a

DISCUSSION

It is assumed that due to the public interest in this species, most sightings have been reported either to the media, or to interest groups in the Bahamas, and therefore we believe the density of killer whales in the Bahamas to indeed be very low, as per our sighting record data. It is unknown whether killer whales historically occurred in this area in low density. Although there is no record of killer whales preying on the Caribbean monk seal (Monachus tropicalis), the commercial over-exploitation during the 1800s (Kenyon, 1977) of this potential prey species may have contributed to a decline in killer whale abundance in the Bahamas. Overall the low density of marine mammal prey in the tropics probably means that the area can no longer support an abundance of marine-mammal eating killer whales, if in fact it ever did. The mean group size reported here is similar to that Fig. 2. A young killer whale with a dwarf sperm whale (Kogia sima) in its reported for groups of killer whales off mouth off Abaco, the Bahamas (sighting 21, 27 July 2005). on seals (Beck et al., 2011) as well as other studies of 4 charlotte dunn and diane claridge

marine-mammal eating killer whales from warm water their photographs and video. We would also like to thank environments, e.g. Hawaii (Baird et al., 2003). Small group Todd Pusser and Leigh Hickmott for help with field obser- size is suggested to be optimal for foraging success on marine vations, sighting reports and matching animals; and mammals (Baird & Whitehead, 2000), and our observations Stephanie King and Kim Parsons for helpful comments support this suggestion for tropical killer whales in the upon review of early drafts of the manuscript. Atlantic. Indeed, marine mammals appear to form significant prey for killer whales in the Bahamas, and particularly Kogia sp. The lack of vocalizations produced by killer whales recorded during this study provides further support that REFERENCES that they may be targeting marine mammals as prey. By delib- erately displaying stealth behaviour and remaining silent Andrews R.D., Pitman R.L. and Ballance L.T. 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